High speed peroxide textile bleaching process



HIGH SPEED PEROXIDE TEXTILE BLEACHING PROCESS Walter F. Coleman, Evanston, Ill., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application April 26, 1956 Serial No. 580,731

13 Claims. (Cl. 8111) This invention relates to the treatment of fibers of vegetable origin and more particularly to an improved, rapid and efiicient method for bleaching textile goods of vegetable origin.

This application is a continuation-in-part of my pending application Serial No. 442,430, filed July 9, 1954, now abandoned.

Goods of the above type have been bleached by heating them in bleach solutions containing peroxygen compounds. Bleaching has usually been preceded by one or more scouring treatments effected using kiers in which the goods were heated, e. g., boiled at atmospheric or higher pressure, for several hours in a strongly alkaline solution. Kier scouring and bleaching methods, often carried out in several applications, have long been considered unsatisfactory because of the prolonged time and cumbersome equipment required.

Scouring and bleaching have more recently been carried out by steaming the goods dampened with the treating solution, then storing the goods in the hot damp condition for the required time. Continuous methods of this type in which the goods have been stored in J-boxes are used extensively. The usual commercial system includes one J-box for the scouring stage and one for the bleaching stage, the storage time in each being at least 1 hour. Such methods are not entirely satisfactory because of the relatively slow processing rate and large volume of fabric in process at any one time.

It has also been proposed to scour or bleach goods of this type by storing them several hours at ordinary temperature while dampened with the treating solution, then steaming the goods. Still other damp storage procedures have been suggested but all such methods require long treating periods and bulky storage facilities.

It is an object of the invention to provide an improved method for bleaching fibers of vegetable origin. A particular object is the provision of a highly efficient and very rapid method for bleaching textile goods of vegetable origin by means of peroxygen compounds. A still further object is to provide a method whereby such goods can be satisfactorily bleached in a matter of seconds. Other objects will be apparent from the following description.

The objects of the invention are accomplished by heating fibers or goods of vegetable origin while they are dampened with an aqueous bleach solution of a peroxygen compound at a temperature considerably above the atmospheric boiling point of water. This heating treatment may be preceded by other treatments, particularly treatments which do not require extended treating periods or bulky storage facilities. Thus, it may be preceded by a similar heating treatment in which the fibers or goods are heated while dampened with a strongly alkaline aqueous solution, or the goods may first be thoroughly wet-out with an aqueous solution of a wetting agent.

The statement that the fibers or goods are heated while they are dampened with a treating solution is used to mean that there is present in the fibers or goods during the heating period an amount of the treating solution equal ice to not more than about %,e. g., 50150% and preferably 70-120%, of the dry weight of the fibers or goods. Damp, dampened and like terms similarly have references to fibers or goods which contain liquid such as treating solutionin an amount within the above range.

It is essential that temperatures considerably above the atmospheric boiling point of water be employed when heating the goods while dampened with the peroxide bleach solution in accordance with the invention. It has been found that when such temperatures are used, highly satisfactory results can be achieved in very short times and without damage to the goods. Temperatures of 275 to 350 F. will most generally be used, the preferred range being 290 to 325 F. Temperatures considerably above 350 F., e. g., up to 400 F. and possibly higher, can be used so long as the chosen temperature is not so high as to cause thermal decomposition or degradation of the fibers. At a temperature of about 300 F., very satisfactory bleaching can be achieved in a time at that temperature of around 10 seconds, disregarding the time required to saturate the fibers with the bleach solution. The time required for satisfactory bleaching increases somewhat as lower temperatures are used but usually will not exceed one minute and will generally not exceed 30 seconds if temperatures no lower than 290 F. are used. With such short heating periods, bleaching can be effected continuously and on large scale without need for bulky storage equipment such as J-boxes and the like required in prior methods to handle the large volume of fabric in process at any one time.

When the present high temperature damp bleaching treatment is to be preceded by an alkaline treatment, a preferred procedure is to carry out the alkaline treatment by heating the goods while dampened with a strongly alkaline aqueous treating solution under substantially the temperature and time conditions described above for the bleaching treatment. By using a temperature of at least 275 F., heating times of not more than 60 seconds are generally adequate to obtain satisfactory bleaching in the subsequent bleaching step, and at temperatures of 290 F. or higher, e. g., 290 to 325 F., times of not more than 30 seconds and as short as 5 to 10 seconds are usually adequate. Thus, under the preferred temperature conditions, the two heating treatments can be effectively carried out in heating times not exceeding a total of 30 seconds, and frequently less than 30 seconds.

The heating times required to give satisfactory bleaching will depend somewhat upon the concentration of the active ingredients in the treating liquids. In general, the lower the concentration of alkali in the liquid for the first treatment (if a high temperature damp alkaline treatment as described above is to precede the bleaching treatment), the longer is the heating time required to obtain full bleaching. With liquid having an alkali concentration equivalent to 2 to 4% caustic soda, as is preferred, heating times for the damp alkaline treatment of around 30 seconds or less are generally satisfactory at temperatures of 290 F. and higher. Higher alkali concentrations, e. g., up to and above about 6% caustic soda, permit shorter times at a given temperature while lower concentrations, e. g., down to about 1%, require longer times. Any of the strongly alkaline materials commonly used in treatments for preconditioning cotton prior to bleaching can be used as the alkalizing agent in preparing the treating solution. Examples of such materials are the alkali metal hydroxides, soda ash, borax, sodium silicate, tri-sodium phosphate and combinations thereof. Sodium hydroxide is preferred because of its cheapness and high effectiveness.

The concentration of peroxygen compound in the bleaching solution usually will be in the range 0.05 to 3% or higher, calculated as H 0 the preferred range being Latina supra 0.2 to 1.5%. Other conditions being equal, the higher the concentration of the peroxygen compound, the shorter will be the time necessary for heating the goods dampened with the bleach solution in order to obtain a full bleach. Hydrogen peroxide and sodium peroxide are preferred peroxygen compounds for use in the bleach solution. However, q hggggtpppunds such as the alkali metal percarbonates, perboTtesTphosphate perhydrates and the like, which are known to yield hydrogen peroxide in aqueous solution, and also the peracids such as peracetic acid and performic acid and the'i'r salts fc ah be uscd. In. addition to the peroxygen compound, the bleach solution preferably will also contain an alkali such as one or more of the alkaline compounds mentioned previously. Use of solutions having an alkalinity of around pH 10 to 11.5 are especially effective, particularly when they include a material such as sodium silicate which functions as a buffer and a stabilizer for the solution of the peroxygeu compound. Sodium silicate concentrations equivalent to about 0.5 to of 42 B. material Na O, 25% SiO and 65% H O) are quite satisfactory. Phosphates and magnesium salts may also be used as stabilizers.

The bleach solution may also include a wetting agent, examples of which are soaps, sulfonated mineral oils, sulfonated higher fatty acids or alcohols and esters thereof, the sodium and similar salts of such sulfonated or sulfated products, the alkoxylated aryl polyether alcohols, polyethylene oxide condensates and fatty alkylol amine condensates. However, it is not essential that a wetting agent be present in the bleach solution.

When the bleaching treatment is not to be preceded by an alkaline treatment as indicated above, it will often be advantageous, although not essential, to wet-out the goods thoroughly with an aqueous solution of a wetting agent. This can be simply and effectively accomplished by immersing the goods in the solution of the wetting agent for a few minutes, after which the goods are preferably thoroughly rinsed. The wet-out can be carried out at ordinary temperatures, but temperatures of 120 to 212 F. are preferred and those of 140 to 212 F. are most preferred. Any of the commonly used wetting agents such as those mentioned above are suitable for use in such a wet-out solution.

It is also preferred in such a wet-out treatment, if used, that the wet-out solution also contain a water-soluble molecularly dehydrated phosphate. The sodium phosphates of this class, such as the sodium pyrophosphates, sodium hexametaphosphate ((NaPO sodium tripolyphosphate (Na P O and Na P O -6H O) and sodium tetraphosphate (Na P O are preferred for availability and cost reasons.

In the above wet-out treatment, the concentration of the wetting agent (and of the phosphate, if used) in the solution employed generally will range from about 0.1 to 1.0%, and preferably will be in the range 0.3 to 0.5%. Concentrations above 1% may be used but show little or no added advantage.

The fibers or goods will preferably be washed or rinsed thoroughly after each treatment whether single or multitreatments are used.

The invention is illustrated by the following examples. In the examples and elsewhere, all percentages of reagents are percentages by weight, based upon total solution weights, unless stated to be otherwise. All aborbency values reported represent the times in seconds for the absorption on the taut surface of the fabric, held in embroidery hoops, of one drop of water delivered from an eye dropper held two inches above the surface (standard method of the American Association of Textile Chemists and Colorists). The brightness values were determined on eight layers of the cloth sample using the kell-known and widely used Hunter multi-purpose reflectance meter. Use of such an instrument for measurements of this type is described in Bureau of Standards Research Paper RP-1345.

Example I A light-weight (0.17 lb./ sq. yd.) muslin in the gray state was desized by an over-night enzyme treatment at F. A number of samples of the desized material were dampened with a 3% caustic soda solution by immersing them in the solution and squeezing out excess solution until the solution retained equaled the dry weight of the sample (liquor to goods ratio of 1:1). The samples were then subjected to the action of live saturated steam in an autoclave at 52 p. s. i. g. The temperature of the samples rapidly reached the temperature (300 F.) of the steam and were held at that temperature for only 5 seconds. After washing thoroughly 5 times with distilled water, the samples were immersed in a bleach solution containing 0.9% H 0 1% 42 B. sodium silicate solution (10% Na O, 25% SiO 65 H 0) and sufficient caustic soda to give a pH of 10.7, then wrung out so as to give a liquor to goods ratio of 1:1. The samples so dampened with the bleach solution were then returned to the autoclave and again heated for only 5 seconds at the temperature of saturated steam at 52 p. s. i. g. (300 F.). After washing, drying and ironing on a mangle, the samples were found to have brightnesses ranging from 90.6 to 91.8 and an absorbency not greater than 1 second. Mote removal was essentially complete in all samples.

Example 2 The experiments of Example 1 were repeated except that the pH of the bleach solution used was adjusted to 11.2 by the addition of caustic soda. Substantially the same results were obtained execpt that the brightnesses were somewhat higher, ranging from 91.4 to 92.7.

In other experiments carried out as described in Examples 1 and 2, cotton threads dyed with Naphthol Red were included along with the gray muslin samples. No dye fading or bleeding occurred.

In still other experiments, it was found that heavy Pequot sheeting (1.7 yds./lb.) could be satisfactorily bleached by the method of the above examples.

Example 3 A light weight muslin in the gray state was desized as in Example 1, immersed directly in a bleach solution containing about 0.9% H 0 1%of a 42 B. sodium silicate solution and sufiicient caustic soda to give a pH of 10.7, then wrung out so as to give a liquor to goods ratio of about 1:1. The fabric so dampened with the bleach solution was subjected immediately in an autoclave to the action of live saturated steam at 300 F. for 30 seconds, then washed and ironed. The treated fabric had a brightness of 86.2 and an absorbency of 1.5 seconds, and mote removal was good.

Example 4 Cotton mulsin in the gray state was wet-out for 2 to 3 minutes at 158 to 212 F. with a 0.2% solution of a commercial alkyl sulfate wetting agent which also contained 0.3% of sodium pyrophosphate. The wet-out fabric was rinsed thoroughly, extracted for 5 minutes at about 212 F. with a 6% aqueous solution of caustic soda to which 0.2% formamidine sulfinic acid had been added. The extracted fabric was rinsed thoroughly then impregnated at a liquor to goods ratio of 1:1 with a bleach solution having a pH of 10.1 and containing 0.8% H 0 1.5% of a 42 B. sodium silicate solution. The impregnated fabric was subjected immediately to the action of live saturated steam under pressure at 275 F. for 30 seconds, then washed and ironed. The treated fabric was motefree and highly absorbent and had a brightness of 86.7.

Example 5 Cotton muslin in the gray state was wet-out as in Example 4, rinsed, extracted for 5 minutes at about 212 F. with a 3% caustic soda solution to which 0.2% of formamidine sulfinic acid had been added, rinsed, then impregnated at a liquor to goods ratio of 1:1 with a bleach solution having a pH of 10.4 and containing 0.8% H 0 and 2.8% of a 42 B. sodium silicate solution. The impregnated fabric was subjected immediately to the action of live saturated steam under pressure at 277 F. for 40 seconds, then washed and ironed. The treated fabric was mote-free and highly absorbent, and had a brightness of 89.4.

Tensile strength and fluidity (cupra-ethylene diamine method) tests'on cotton goods processed as illustrated in the examples gave values which are normal for bleached cotton, showing that no abnormal damage resulted from the treatments despite the high temperatures used.

Cotton goods are usually processed to a brightness averaging about 86.5 and a water absorbency averaging about 2.5 seconds. Long conditioning treatments with strong alkali were, heretofore, almost invariably regarded as necessary to obtain satisfactory absorbency and mote removal, and bleaching times on the order of one hour up to several days were usually necessary to obtain satisfactory brightness. It was, therefore, quite surprising that brightnesses of about 86.5 and higher and absorbencies of 2.5 seconds or better with substantially complete mote removal could be readily obtained in the very short bleaching times characteristic of the present method. Complete mote removal with a brightness of 90 or higher and an absorbency of about one second or less can be readily obtained by the present method under preferred conditions. Because of the short times involved, no special storage equipment such as the customary kiers, J-boxes or storage bins, necessary in prior methods, is needed in practicing the present method. The elimination of such equipment, the great reduction in the space required for equipment and in processing time, and the consequent great reduction in the amount of goods in process at any one time, are highly practical advantages of the present method over prior methods.

Dampening of the fibers such as textile goods with the treating solution for the high temperature damp treatments described is conveniently eifected by saturating the fibers with the solution, e. g., by immersing them in the solution, then removing excess solution if necessary, e. g., by wringing, squeezing or hydro-extracting, until the fibers retain the desired amount of solution. Dampening may also be efiected by spraying, dipping, padding or any other equivalent known dampening method.

The high temperature damp heating treatments should be efiected under conditions which prevent drying out of the fibers to any substantial extent and this is most conveniently accomplished by heating the fibers directly with saturated steam at a steam pressure which will result in the desired temperature. In continuous operations, e. g., when continuous length textile goods are to be bleached, the goods, after being dampened with the treating solution, can be conveniently drawn continuously, for example, in openwidth form through a chamber or zone filled with saturated steam at a pressure corresponding to the desired temperature. The rate of travel of the goods through the chamber will be consistent with the heating time desired and can be much faster than is permissible in present continuous methods. Pressure in the chamber can be maintained as desired through the use of well-known mechanical or liquid seals at the points of entry and exit of the goods.

The method of the invention is effective in the bleaching of natural or regenerated fibers of vegetable origin generally. It is particularly well suited for bleaching textile goods such as cotton, linen and the like. The fibers may be in their natural or gray state, or they may have been previously preconditioned by any of the wellknown scouring, souring, desizing, boiling or other treatments. Because of the high efiectiveness of the method in treating gray goods, particularly those of cotton, the the usual scouring methods employing long treating times are most preferably avoided. Goods containing portions colored with naphthol dyes can also be bleached by the present method without danger of color fading or bleeding.

Gray state and gray goods are terms used herein to designate cotton or other fibers or goods of vegetable origin which have not been preliminarily treated, e. g., scoured, to remove ligneous, fatty and pectinous materials originally associated with cellulose.

I claim:

1. The method of bleaching a cotton textile comprising dampening said textile with from 50 to of its dry weight of an aqueous alkaline solution containing a peroxygen compound at a concentration equivalent to from 0.05 to 3% hydrogen peroxide, and bleaching said dampened textile in a time period not exceeding 60 secends by subjecting the dampened textile during said period to the direct action of saturated steam at a temperature of from 275 to 400 F. and at a pressure corresponding to said temperature.

2. The method of claim 1 wherein the temperature is 275 to 350 F. A

3. The method of claim 2 wherein the temperature is 290 to 325 F.

4. The method of claim 3 wherein the time period does not exceed 30 seconds.

5. The method of claim 1 wherein the textile is first wet-out in an aqueous solution of a wetting agent.

6. The method of bleaching a cotton textile comprising dampening said textile with from 50 to 150% of its dry weight of an aqueous hydrogen peroxide solution having a pH of from 10 to 11.5 and containing from 0.05 to 3% hydrogen peroxide, and bleaching the dampened textile during a time period not exceeding 60 seconds by subjecting the dampened textile during said period to the direct action of saturated steam at a temperature of from 275 to 400 F. at a pressure corresponding to said temperature.

7. The method of claim 6 wherein the temperature is 290 to 325 F. and the time period does not exceed 30 seconds.

8. The method of claim 6 wherein the solution contains from 0.2 to 1.5% hydrogen peroxide.

9. The method of bleaching a cotton textile comprising dampening said textile with from 50 to 150% of its dry weight of an aqueous solution containing alkali equivalent to from 1 to 6% caustic soda, then subjecting the dampened textile to the direct action of saturated steam at a temperature of from 275 to 400 F. and at a pressure corresponding to said temperature; dampening the so-treated textile with from 50 to 150% of its dry weight of an aqueous alkaline hydrogen peroxide solution containing from 0.05 to 3% hydrogen peroxide, and bleaching the textile dampened with the hydrogen peroxide solution by subjecting it to the direct action of saturated steam at a temperature of from 275 to 400 F. and at a pressure corresponding to said last named temperature, the time periods for both of said steaming treatments not exceeding a total of 60 seconds.

10. The method of claim 9 wherein the alkaline hydrogen peroxide solution has a pH of from 10 to 11.5.

11. The method of claim 10 wherein the temperature during each steaming treatment is from 290 to 325 F. and the time periods for both of said steaming treatments do not exceed a total of 30 seconds.

12. The method of bleaching a cotton textile comprising dampening a cotton textile in the gray state with from 50 to 150% of its dry weight of an aqueous solution containing alkali equivalent to from 1 to 6% caustic soda, then steaming the dampened textile with saturated steam at a temperature of from 290 to 325 F. and at a pressure corresponding to said temperature; dampening the s0 treated textile with from 50 to 150% of its dry weight of an aqueous solution of hydrogen peroxide having a pH of 10 to 11.5 and containing from 0.05 to 3% hydrogen peroxide, and bleaching the textile dampened with the hydrogen peroxide solution by steaming it with saturated steam at a temperature of from 290 to 325 F. and at a pressure corresponding to said last named ternperature, the time periods for both of said steaming treatments not exceeding a total of 30 seconds.

13. The method of bleaching a cotton textile comprising dampening said textile in the gray state with from 50 to 150% of its dry weight of an aqueous hydrogen peroxide solution having a pH of from 10 to 11.5 and containing 0.2 to 1.5% hydrogen peroxide, and bleaching the dampened textile by steaming it for a time period not exceeding 30 seconds with saturatedsteam at a temsponding to said temperature.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES I. of the Soc. of Dyers and Colourists, September 1952, pp. 337-344.

Marsh, J. T.: Introduction to Textile Bleaching, Chapman and Hall, London, 2nd impression 1948, pp. 

9. THE METHOD OF BLEACING A COTTON TEXTILE COMPRISIN DAMPENING SAID TEXTILE WITH FROM 50 TO 150% OF ITS DRY WEIGHT OF AN AQUEOUS SOLUTION CONTAINING ALKALI EQUIVALENT TO FROM 1 TO 6% CAUSTIC SODA, THEN SUBJECTING THE DAMPENED TEXTILE TO THE DIRECT ACTION OF SATURATED STEAM AT A TEMPERATURE OF FROM 275 TO 400%F. AND AT A PRESSURE CORRESPONDING TO SAID TEMPERATURE; DAMPENING TO SO-TREATED TEXTILE WITH FROM 50 TO 150% OF ITS DRY WEIGHT OF AN AQUEOUS ALKALINE HYDROGEN PEROXIDE SOLUTION CONTAINING FROM 0.05 TO 3* HYDROGEN PEROXIDE, AND BLEACHING THE TEXTILE DAMPENED WITH THE HYDROGEN PEROXIDE SOLUTION BY SUBJECTING IT TO THE DIRECT ACTION OF SATURATED STEAM AT A TEMPERATURE OF 275 TO 400*F. AND AT A PRESSURE CORRESPONGING TO SAID LAST NAMED TEMPERATURE, THE TIME PERIODS FOR BOTH OF SAID STEAMING TREATMENTS NOT EXCEEDING A TOTAL OF 60 SECONDS. 